Roper St. Francis Hospital 1 article published in JoVE Biochemistry A G-quadruplex DNA-affinity Approach for Purification of Enzymatically Active G4 Resolvase1 Eric D. Routh*1, Steven D. Creacy*2, Peter E. Beerbower3, Steven A. Akman4, James P. Vaughn1, Philip J. Smaldino3 1Department of Cancer Biology, Wake Forest School of Medicine, 2YX Genomics, 3Department of Biology, Ball State University, 4Department of Hematology and Oncology, Roper St. Francis Hospital G4 Resolvase1 binds to G-quadruplex (G4) structures with the tightest reported affinity for a G4-binding protein and represents the majority of the G4-DNA unwinding activity in HeLa cells. We describe a novel protocol that harnesses the affinity and ATP-dependent unwinding activity of G4-Resolvase1 to specifically purify catalytically active recombinant G4R1.